I'm confused when it comes to defining homeotherms, heterotherms, endotherms, and ectotherms. I've done some Googling and looking through my university textbook to try and distinguish between homeothermic and endothermic (and heterothermic vs. ectothermic) but I always seem to come across the same definition for both. The definitions I've found for homeotherms and endotherms seem to be the exact same but that's obviously not the case otherwise how can we have a partially ectotherm and partially homeotherm (like most marine fish).

I'm really not sure about this so hopefully someone can confirm or correct me but...

Homeotherms maintain a constant internal temperature.

Heterotherms have varying body temperatures.

Endotherms are able to produce heat internally (though, if I've learned correctly some animals classified as ectotherms do as well, but are not considered endotherms due to relatedness; or maybe I'm just confusing a taxanomic grouping with the term...)

Ectotherms are unable to control heat internally and so rely on their environment.

Generally the homeothermic organisms are also endotherms, but it is possible to have an ectotherm that through behavior manages to keep a constant body temperature. The reverse does happen as well: some varieties of bats drop their metabolism (and with it, internal temp.) when not actively hunting, this would mean they are both an endotherm (internal heat producer) and a heterotherm (variable internal heat)...

To add a question; it seems that most ectotherms are more specifically 'Poikilotherms.' However I was unable to find anything to explain what the difference between the 2 was... anyone?

Yes, what you said makes sense! I'm not sure why I didn't think of this before, but the fact that homeotherms are able to maintain a constant core body temperature explains why homeothermic endotherms have a thermal neutral zone whereas heterothermic endo-/ecto-therms do not.

I had a pretty solid definition for endotherms and ectotherms but I just couldn't distinguish those two definitions with homeotherms and heterotherms, so thanks a lot!

As for your question, I don't think poikilotherms is compared to endo-/ecto-therms but rather homo-/hetero-therms. If I remember correctly, my lab TA told my lab section that poikilotherms have body temperatures that are completely dependent upon the environment whereas heterotherms, although affected by environmental temperatures, have varying degrees of metabolic heat production and are able to somewhat control their body temperatures.